The invention relates to an exhaust gas system, such as for an internal combustion engine and especially for a diesel engine. The invention can be applied in vehicles and especially in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles. The invention further relates to a vehicle comprising the exhaust gas system for recuperation of waste heat of an internal combustion engine comprised in the vehicle.
The exhaust gas system comprises an arrangement for conveying an exhaust gas stream. The arrangement for conveying an exhaust gas stream may comprise an exhaust after treatment system. The exhaust gas system further comprises a thermodynamic engine connected to the exhaust gas stream conveying arrangement for recovery of heat from the exhaust gas stream. The thermodynamic engine comprises a working fluid circulation circuit.
More specifically, the thermodynamic engine is configured for converting thermal energy of a gaseous phase working fluid into kinetic energy, and may be constituted by a Rankine cycle engine.
According to the state of the art, it is known to use such thermodynamic engines, particularly Rankine cycle engines, for recuperation of waste heat of internal combustion engines. As commonly known, a Rankine cycle engine is an engine that converts heat into work. The heat is applied externally to a preferably closed working fluid circuit which may use water or other suitable liquids as working fluids. A pump is used to pressurize the liquid working fluid received from a condenser which is then heated and thereby converted into its gaseous phase. Subsequently, the gaseous working fluid is transported to a steam engine, where the thermal energy is convened to kinetic energy. In a further step the gaseous working fluid is converted back to its liquid phase in the condenser.
A common working fluid is water as it is easy to supply, already present on a vehicle and harmless to the environment. Even if water has some attractive properties, it also has some drawbacks.
For example, water freezes at 0° C and if the steam is mixed with air, the functionality of the steam engine drops. Additionally, small amounts of air in the steam can be rather aggressive to the construction material.
For avoiding air accumulating in the steam it has been suggested to keep the pressure in the working fluid above ambient air pressure. Disadvantageously, this results in a constraint in the efficiency, since the condensing temperature needs to be relatively high (particularly above 100 degree Celsius). However, during a longer standstill (night, weekend, etc.) it is difficult to avoid a pressure drop below ambient pressure in the system, which in turn results in air leaking into the system.
Further, in some designs it is even preferred to have lower pressure than ambient pressure in some parts of the Rankine cycle for a good efficiency.
For solving the freezing problem, it has been suggested to mix the water with small amounts of ammonia or alcohol, so that the freezing point is lowered. Additionally, ammonia or alcohol also lowers the dewpoint so that the condensing can be performed at lower temperatures.
Disadvantageously, ammonia is both caustic and hazardous. Therefore, ammonia has to be handled with great care and should not be released to the environment. However, such a release is necessary for instance in case of an accident involving the thermodynamic engine or a vehicle comprising such an engine (e.g. a collision of the vehicle with another vehicle) or during maintenance of the thermodynamic engine and/or of the vehicle. Up to now, a bypass of the expander device is used for releasing the pressure in the working fluid and providing safe maintenance possibilities. Disadvantageously, this procedure is very time consuming so that stand-still, periods of the vehicle in a workshop are unnecessarily prolonged and/or waiting times for safe access to a vehicle, for e.g., a rescue team, are unacceptable long.
It is desirable to provide an exhaust gas system, which is useable for recovering waste heat from an internal combustion engine which provides a safe release possibility of the working fluid to the environment.
Accordingly, an exhaust gas system is provided comprising an arrangement for conveying an exhaust gas stream and a thermodynamic engine connected to the exhaust gas stream conveying arrangement for recovery of heat from the exhaust gas stream. The thermodynamic engine comprises a working fluid circulation circuit. The exhaust gas system comprises at least one working fluid release means, which is connected between the working fluid circulation circuit and the exhaust gas conveying arrangement for releasing the working fluid from the working fluid circulation circuit to the exhaust gas conveying arrangement. More specifically, the exhaust gas stream conveying arrangement comprises at least one exhaust gas treatment unit and the working fluid release means is connected upstream of or directly to the exhaust gas treatment unit.
Thereby, the working fluid release means creates conditions for releasing at least part of the working fluid to the exhaust gas treatment unit which renders the working fluid harmless to the environment. The working fluid release means may alternatively be called venting means.
Further, the exhaust gas system creates conditions for reducing the air accumulation tendency of the thermodynamic engine due to ambient air leaking into the system.
Advantageously, thereby a safe release of the working fluid is possible. The exhaust gas system creates conditions for a quick and safe pressure relief Additionally, by providing a safe release, the use of ammonia is possible, so that at least freezing of the working fluid at cold, temperatures may be avoided.
Additionally, the thermodynamic engine can easily be purged from accumulated air. If additionally a working fluid is used which is already present in the exhaust gas system, the overall parts in the system can be reduced, which in turn is cost- and space efficient. In the application of a vehicle, it would increase the load capacity.
Preferably, a catalytically working treatment unit is used. According to a preferred embodiment, the exhaust gas treatment unit is formed by a selective catalytic reduction unit (SCR) using ammonia for reducing a NOx amount of the exhaust gas.
In other words, the working fluid is not released directly to the atmosphere but to a catalytic treatment unit which converts the working fluid to harmless compounds, in a preferred application, such a catalytic treatment is provided by the exhaust gas after treatment system of a vehicle equipped with an internal combustion engine. The synergistic effects provided thereby allow for a system which provides a release of working fluid without problems as well as a recuperation of waste energy of the internal combustion engine.
As mentioned above, the exhaust gas after treatment system may convert hazardous working fluids into harmless compounds. Particularly, the use of ammonia, preferably in form of urea, is advantageous as ammonia may be used as reduction agent in the exhaust gas after treatment system and can also be used as working fluid for a thermodynamic engine. Thereby, the overall number of parts at the vehicle can be reduced.
Using ammonia has the further advantage that surplus ammonia from the working fluid circuit can be used in the exhaust gas after treatment system, particularly the SCR unit. Thereby no extra reservoir for collecting surplus ammonia needs to be provided.
According to a further preferred embodiment, the thermodynamic engine comprises a condensation device positioned in the working fluid circulation circuit and the working fluid release means is connected to the condensation device at a gas side thereof. Advantageously, thereby accumulated air may be removed from the condensation device, whereby in turn malfunctions of the condensation device and/or of other parts of the thermodynamic engine are avoided.
According to a further preferred embodiment, the thermodynamic engine further comprises a heating device for heating the working fluid and thereby converting a liquid working fluid to the gaseous phase working fluid. Especially, the heating device of the thermodynamic engine is formed by a heat exchanger positioned in the exhaust gas stream for exchanging heat between the exhaust gas stream and the working fluid of the thermodynamic engine. This creates conditions for recovery of heat from the exhaust gas stream by means of the thermodynamic engine.
According to a farther development, the heating device of the thermodynamic engine is arranged downstream of the exhaust gas after treatment unit in the exhaust gas stream. For not cooling the exhaust gas before the exhaust gas has entered the exhaust gas after treatment system and thereby compromising the efficiency of the exhaust gas after treatment system, the heat exchanger is preferably arranged downstream of the exhaust gas after treatment system.
According to a further preferred embodiment, the working fluid release means is connected to the working fluid circuit downstream of the heating device and upstream of a gas liquid interface in the condensation device. Preferably, the working fluid release means is connected to the working fluid circuit also upstream of the expander device. Under certain circumstances, at the high pressure side, namely upstream of the expander, the pressure of the working fluid may become too high so that a release of the working fluid is necessary. Since the pressure of the working fluid upstream of the expander unit is usually higher than the pressure in the exhaust gas duct, additional propelling means for transporting the working fluid to the exhaust gas duct are not required.
According to a further preferred embodiment, the thermodynamic engine further comprises a pump device for circulating the working fluid; an expander device for converting thermal energy of the gaseous phase working fluid into kinetic energy; and that the condensation device is arranged downstream of the expander device for cooling and thereby converting the gaseous phase working fluid into the liquid phase.
According to a further preferred embodiment, the working fluid release means comprises a connecting duct and at least one release valve for controlling opening and/or closing of the connecting duct. This valve may be an On-Off valve which is normally closed, but it can also be any other suitable valve, e.g. a valve with variable inner diameter for gradually controlling the amount of working fluid streaming through of the working fluid circuit.
According to a further preferred embodiment, the exhaust gas system comprises a control unit, which is operatively connected to the release valve for opening and/or closing the valve.
According to a further preferred embodiment, the exhaust gas system comprises at least one pressure detector arranged in the working fluid circuit and that the control unit is operatively connected to the, pressure detector for controlling the opening and/or closing of the release valve in dependence on a detected pressure. By controlling the valve in dependence of the detected pressure, the pressure in the working fluid circuit can be controlled and safety compromising situations, such as over-pressure in the working fluid circuit, can be avoided. Preferably, the pressure detector is arranged downstream of the heating device and upstream of a gas-liquid interface in the condensation device. Further preferably, the control unit is configured to open the release valve if a pressure exceeding a pressure threshold is detected by means of the pressure detector.
Since safety compromising pressure situations mostly appear at the high pressure side of the working fluid circuit and particularly upstream of the expander unit, detecting and controlling the valve in dependence of the pressure upstream of or at the expander device is advantageous.
According to a further preferred embodiment, the exhaust gas system comprises at least one air sensor fir detecting air in the working fluid circuit, that the control unit is operatively connected to the air sensor for opening the valve upon detection of air accumulation in the working fluid circuit. Alternatively or additionally, the control unit may be operatively connected to a collision warning system, detecting a potential collision, and/or a collision detection unit, detecting a collision, for opening the venting valve upon detection of a risk for a collision or a collision.
According to a further preferred embodiment, the exhaust gas system comprises a manually operable means, which is connected to the control unit for manually controlling opening and/or closing of the valve.
Advantageously, in a safety compromising situation, such as a collision for instance of the vehicle comprising such a thermodynamic engine, the working fluid may be released instantaneously so that a non-hazardous access to the vehicle is possible. The manual release possibility even provides a higher safety since in case the control unit is damaged a release of the working fluid is still possible.
According to a further preferred embodiment, the exhaust gas system comprises a working fluid storage tank fluidly connected to the working fluid circuit for storing liquid working fluid. Preferably, the working fluid storage tank is fluidly connected to a low pressure side of the working fluid circuit. The working fluid storage tank is preferably configured for providing liquid working fluid to the working fluid circuit by means of a supply duct. Further preferably, the thermodynamic engine comprises a condensation device positioned in the working fluid circulation circuit and the working fluid storage tank is connected to the working fluid circuit downstream of the condensation device and upstream of the heating device. Due to working fluid leakage during normal operation and due to a potential release of working fluid through the venting means, replacement of working fluid in the working fluid circuit may be required. By the virtue of energy saving reasons, the working fluid is preferably supplied in its liquid phase to the low pressure side of the working fluid circuit.
Preferably, the working fluid storage tank is fluidly connected to a high pressure side of the working fluid circuit. Especially, the exhaust gas system comprises a working fluid storage tank valve configured to control working fluid flow between the working fluid storage tank and the working fluid circuit. Further preferably, the exhaust gas system comprises a control unit and that the working fluid storage tank valve is connected to the control unit in order to open if a pressure below ambient air pressure is detected in the working fluid circuit.
According to a further preferred embodiment, the working fluid release means comprises a first connection duct fluidly connecting the low pressure side of the working fluid circuit to the working fluid storage tank and a second connection duct connecting the working fluid storage tank to the means providing ambient air pressure preferably to the exhaust gas side of die internal combustion engine. Thereby, the amount of working fluid emitted into the exhaust gas may be reduced as the gaseous working fluid condenses in the cool liquid working fluid of the storage tank and only accumulated air is transported off to the exhaust gas duct. Consequently, the working fluid storage tank can be made smaller and/or requires less frequent refills.
Preferably, the working fluid may be water and/or ammonia, and/or more generally a mixture of a first component and a second component, wherein preferably the first component is water and the second component is an antifreeze component, such as ammonia, alcohol or a mixture thereof. According to a thither preferred embodiment, the working fluid comprises an antifreeze component, such as ammonia and/or alcohol, such as ethanol. Using alcohol, ammonia and/or a mixture of alcohol or ammonia with water lowers the freezing point, whereby an anti-freeze protection for the thermodynamic engine is provided. The use of ammonia has the additional advantage that ammonia may already be present in a vehicle, preferably in the form of urea, as reduction agent for the reduction of NOx in the exhaust gas aftertreatment system thus provision of additional tanks or reservoirs may be avoided.
It is also desirable to provide an exhaust gas system, which creates conditions for working properly in different environments, especially in different climates.
Accordingly, an exhaust gas system is provided comprising a thermodynamic engine, wherein the thermodynamic engine comprises a working fluid circulation circuit, wherein the working fluid comprises an antifreeze component. Further, the exhaust gas system comprises at least one reservoir for the antifreeze component, wherein the at least one reservoir is fluidly connected to the working fluid circuit for regulating a concentration of the antifreeze component of the working fluid in the working fluid circuit. The reservoir for the antifreeze component provides the possibility to increase and/or decrease the concentration of antifreeze component in the working fluid circuit.
According to a preferred embodiment, the exhaust gas system comprises an arrangement for conveying an exhaust gas stream and the thermodynamic engine is connected to the exhaust gas stream conveying arrangement for recovery of heat from the exhaust gas stream. Preferably, the exhaust gas stream conveying arrangement comprises an exhaust gas after treatment unit. Especially, the exhaust gas after treatment unit and the thermodynamic engine are connected to the same ammonia reservoir. Since ammonia can he used for the SCR unit as well gas for the working fluid circuit only one ammonia reservoir and thereby only one additional tank is necessary. Additionally, the SCR unit may serve as ammonia storage for storing ammonia released from the working fluid circuit. This reduces, the overall parts of the vehicle and facilitates refilling of the various tanks. Further preferably, the exhaust gas treatment unit is formed by a selective catalytic reduction unit (SCR) using ammonia for reducing a NOx amount of the exhaust gas.
According to a further preferred embodiment, the exhaust gas system comprises a connection duct, which connects the reservoir and the working fluid circulation circuit and/or a valve for regulating a concentration of the antifreeze component of the working fluid in the working fluid circuit. Preferably, the exhaust gas system comprises a controller configured to control the concentration of the antifreeze component by opening and/or closing the reservoir valve in accordance to a local climate zone and/or a sensed ambient temperature.
In case the second component serves as anti-freeze component or generally has influence on the phase transition points of the working fluid, this increase and/or decrease of the concentration of the second component in the working fluid may be triggered by the local climate and/or a sensed ambient temperature. Advantageously, at cold temperatures a high concentration of the second component can be used as anti-freeze protection so that an increased amount of the second component during cold temperatures, i.e. during wintertime, is provided, wherein at higher temperatures a lower concentration is provided so that the condenser can operate at higher temperatures.
Preferably, the concentration of the second component can be adapted on a daily, weekly and/or a monthly basis depending on the expected temperature variations. Of course it is also possible to adapt the concentration of the second component on a shorter time scale or an even longer time scale.
In case the reservoir or the working fluid storage tank is connected to the working fluid circuit upstream of the expander device, supply of an additional amount of working fluid or a additional amount of the second component to the working fluid during shutdown of the combustion engine may prevent air from leaking into the working fluid circuit. Preferably this supply takes place if a pressure below ambient pressure is detected at the nigh pressure side of the circuit so that the additional amount of working fluid may compensate the pressure drop.
In case ammonia is used as second component or working fluid, the reservoir or the working fluid storage tank may be adapted to be heated to a temperature where the ammonia in the reservoir/tank has a pressure above ambient air pressure and/or above the pressure in the working fluid circuit at the connection of the reservoir/tank. This has the advantage that no additional pump is necessary for propelling flow of ammonia, from the ammonia reservoir/tank to the working fluid circuit.
According to a further preferred embodiment, the ammonia reservoir is adapted to store liquid ammonia and/or an ammonia adsorbing material, preferably CaC and/or MgCI2 and/or SRCI2 an ammonia compound preferably urea, ammoniumcarbamate and/or ammoniumcarbonate. Preferably, ammonia adsorbing materials or ammonia compounds are used since working with liquid ammonia calls for additional safety precautions.
According to a further preferred embodiment, the exhaust gas system comprises at least one collecting reservoir, which is connected to the working fluid circuit for collecting working fluid released from the working fluid circuit. Advantageously, the second component, which has been supplied to the working fluid circuit during shut down of the combustion engine and is at surplus in the working fluid circuit after restart of the combustion engine, may be collected in the collecting reservoir. By collecting the surplus second component in the collecting reservoir, the second component is not wasted and frequent refilling can be avoided.
According to a farther aspect of the invention, the thermodynamic engine is part of a heat recovery system, which is adapted to use waste heat of an internal combustion engine. Preferably, the internal combustion engine is connected to an exhaust gas duct which provides exhaust gas from the internal combustion engine to an exhaust gas after treatment system. Advantageously, at least one heating device of the thermodynamic engine is arranged at the exhaust gas duct, preferably downstream of the exhaust gas after-treatment system for heating the working fluid of the thermodynamic engine. Thereby, heat of the internal combustion engine is not wasted but used for the operation of the thermodynamic engine, whereby energy is recovered.
Preferably, for using the waste heat of the combustion engine, the heating device of the thermodynamic engine is at least one heat exchanger which uses the waste heat of the exhaust gas of the internal combustion engine as a heat source. However, it is also possible to connect at least one heat exchanger to a cooling fluid circuit of the internal combustion engine, whereby also waste heat of the combustion engine can be used. Thereby, an energy recovering system is provided which uses already existing parts of a vehicle for providing a maximum efficiency.
According to a further preferred embodiment, the working fluid release means is fluidly connected to the exhaust gas duct of the internal combustion engine, preferably upstream of the exhaust gas aftertreatment system, so that the exhaust gas aftertreatment system provides the at least one, preferably catalytic, unit for (catalytically) treating the working fluid. This embodiment has the advantage that an already existing exhaust gas aftertreatment system may be used for the, preferably catalytic,treatment of the working fluid.
Additionally or alternatively, it is also possible to use the exhaust gas aftertreatment system or at least part of it as working fluid storage, e.g. as the above mentioned collecting reservoir. Particularly, at cold temperatures the exhaust gas aftertreatment system is able to store significant amounts of ammonia, which may be used up later on for the catalytically treatment of the exhaust gas.
According to a further aspect of the invention, a vehicle is provided, which comprises an exhaust gas system according to any one of the alternatives described above, which exhaust gas system is connected to the internal combustion engine. Especially, the internal combustion engine connected to an exhaust gas duct providing a passage for an exhaust gas of the internal combustion engine to the atmosphere, wherein waste heat of the internal combustion engine is used as heat source for propelling the thermodynamic engine. Advantageously, the thermodynamic engine is at least part of a heat recovery system of the vehicle as mentioned above.
Further advantages and preferred embodiments are defined in the claims, the description and the figures.